A shaped charge is an explosive device in which a shell called a liner, commonly a metal hollow cone or hemisphere (forming a hollow, open, “mouth”), which liner is surrounded by a high explosive charge, which charge is enclosed in a casing, which can be manufactured of steel, composites, aluminum or fiberglass, and usually with a detonator for the explosive charge located at the end opposite the hollow open mouth. When the explosive is detonated, a detonation wave is formed as a very high velocity jet that has great penetrative power, i.e. significant explosive momentum. Such devices, with such penetrative power, fulfill significant military and civil needs. The latter includes needs within the oil industry (such as detailed in U.S. Pat. Nos. 4,633,951, 4,683,943, 4,823,875, 5,775,426 and published U.S. Pat. Applications 2003/0037692 and 2005/0056459), ejector seat mechanisms, and also civil engineering work such as decommissioning of large structures.
For military applications, shaped charges were first developed after WWI as an anti-tank device—a device that has developed to include a generally cylindrical charge that lies flat against the target (to provide a direct detonation effect); a hollow conical mouth formed of a liner, to further channel the explosive force or “jet” and to increase the penetrative effect thereof; and an explosive charge on the other side of the liner; which charge is encapsulated within an overall housing. Typically, the jet will reach its terminal velocity within about 40 milliseconds, with an acceleration reaching about 25 million g. The pressure is so great the a velocity of more than 10,000 m/s is achieved—which creates an intense localized force that can have a devastating effect even against modern rolled homogenous armored targets (RHA targets)—causing both plastic deformation and hydrodynamic penetration of the target (i.e. imparting peak pressures in the target armor of up to about 100-200 GPa and temperatures of up to about 500-600 degrees Celsius or more).
Considering the potent forces unleashed by shaped charge devices, as described above, safety becomes a critical issue. A particular High Explosive Anti-Tank (HEAT) round is the Saab Bofors Dynamics AT4, which contains a high explosive, Octol (HMX/TNT)-filled, shaped charge. The fuse to detonate this HEAT round has an out-of-line detonator safety device to prevent accidental initiation, until impact. However, there is nothing to mitigate the jetting effect if the round were subjected to premature, pre-firing, shock—as if struck by an enemy projectile; or, if the round were subjected to an accidental stimulus—such as a fire, or accidental explosion, during production, transport, or storage.
U.S. Pat. No. 5,467,713 provides an ignition and safety device for a grenade projectile provided with a shaped charge insert; wherein such projectiles with shaped charge inserts are disclosed in U.S. Pat. No. 4,969,397). This safety device relates to an arrangement for a base-side impact fuse for such a grenade, which fuse includes a housing for attaching a spin-dependent safety element and an acceleration-dependent safety element for preventing arming of the fuse until the fuse has been subjected to launch acceleration force and to a given centrifugal force—which forces are only present upon launch. This device, as in the case of the Bofors Dynamics AT4 out-of-line detonator safety device, does not mitigate or prevent detonation, if the rounds are subjected to shock or to accidental stimulus.
U.S. Pat. No. 4,673,033 discloses a means of indicating if a string of shaped charges, lowered into a well shaft to complete the “drilling” thereof by perforating into the formation at the bottom of the well shaft, has successfully been discharged—prior to retrieval of the supposedly discharged charges out of the well shaft. This device functions by adding an additional shaped charge to the string of shaped charges, and detecting a signal at the top of the well head, if this extra charge has properly detonated; thereby, clarifying if there is any risk to retrieving any still live charge. Again, this device provides no mitigation or safety, with respect to any pre-use accidental initiation of the shaped charge.
Clearly there is a need in the art for a relatively low cost, simple means of mitigating the exceptional destructive effects of an unintended or accidental detonation of a shaped charge device.